A current sensor is a device that detects electrical current in a conductor and generates an output signal proportional to the detected current. Current sensors can detect either alternating current (AC) or direct current (DC) flowing in the conductor.
Many DC current sensors in the market today use Hall-effect sensors as the primary element for detecting a magnetic field generated by current flowing through the conductor. A Hall-effect sensor is a transducer that varies its output voltage in response to a magnetic field.
Hall-effect sensors can be used in open-loop and closed-loop configurations. Generally speaking, an open-loop Hall-effect sensor uses the Hall voltage directly to produce an output signal. This configuration has the advantage of being simpler to implement, but suffers from a significant amount of nonlinearity. A closed-loop Hall-effect sensor, in contrast, has a coil that is actively driven to produce a magnetic field that opposes the field produced by the current being sensed. In this configuration, the Hall-effect sensor is used as a null-detecting device with the output signal being proportional to the current being driven into the coil, which is proportional to the current being measured. This method is more complex than the open-loop method, but it has the advantage of greatly reducing nonlinearities associated with the Hall-effect sensor itself, since it is essentially being operated at a single point in its range.
With high current DC sensors (e.g. on the order of tens of amperes and above), Hall-effect sensors are typically used in an open-loop configuration due to the large currents that would have to be applied to the coil of a closed-loop configuration. Since Hall-effect sensors are inherently temperature sensitive, the output of an open-loop Hall-effect sensor tends to experience offset and/or linearity drift as its temperature varies.
When a Hall-effect sensor is provided with signal processing to provide relatively low current or voltage outputs (e.g. industry standard 4-20 mA, 0-5 VDC or 0-10 VDC outputs) they are often referred to as “DC current transducers.” Such signal processing tends to be analog in nature, requiring one or more trimming potentiometers (“trim pots”) for proper calibration. While analog circuitry is relatively inexpensive, it suffers from a lack of accuracy in that trims pot tends have a tolerance in the +20% range. Furthermore, manual calibration by adjusting one or more trim pots is a time consuming, and therefore expensive, part of the manufacturing process. Also, analog circuitry is not well adapted to compensate for temperature variations, thereby further increasing the error of the measurement.
These and other limitations of the prior art will become apparent to those of skill in the art upon a reading of the following descriptions and a study of the several figures of the drawing.